The present invention relates generally to aircraft low tire pressure detection systems, and more particularly to a system for detecting and indicating an underpressurized tire on an aircraft landing gear while the aircraft is taxiing or otherwise moving on the ground.
It is extremely important that all of the tires carried by aircraft landing gear are properly pressurized to insure safe and reliable takeoff and landing procedures. Often, this safety consideration requires personnel to visually inspect the landing gear and to measure and check individual tire pressures prior to takeoff. These visual inspections and measurements can be difficult to accomplish under severe conditions such as extreme winter weather.
Moreover, even after the tires pressures have been checked prior to taxiing for takeoff, one or more tires can become underinflated, a dangerous condition which would go undetected by the flight crew. Unequal tire pressures can result in unequal load sharing and tire heating. Aircraft accidents have resulted where it was suspected that one tire was losing tire pressure during taxiing.
A successful system for generating an indication of low tire pressure is shown and described in Bateman U.S. Pat. No. 4,312,042, entitled "Weight, Balance and Tire Pressure Detection Systems", and assigned to the assignee of the instant application. This system utilizes two pairs of inclinometers mounted on a structural member carrying the landing gear tires with the sensitive axes of one pair of inclinometers being disposed at right angles to the sensitive axes of the other pair. The signal outputs from the first pair of inclinometers are subtracted to generate a signal indicating the tilt of the structural member. The signal outputs from the second pair of inclinometers are combined to generate a signal indicating the torsion in the structural member. The tilt and torsion signals are used to locate a particular tire of the set of tires carried by the structural member which is underpressurized.
While the system described above is capable of detecting an underpressurized tire, it has been found that the sensitivity of the system is limited by the variation in parking, taxiway and runway surfaces and slopes. Since the variation in these factors may be extreme, the system must be adjusted to generate a low tire pressure indication when the tire is essentially flat, e.g. when a loss of 130 psi has occurred in a normally inflated 185 psi pressurized tire. However, even when the system is set to detect such a large loss of pressurized air, nuisance warnings of a possible flat tire can occur approximately once every 50 flight segments, chiefly at specific airports and gate positions. It is desirable to reduce this frequency of erroneous indications.